Resistance-size cerebral arteries modulate brain regional blood pressure and flow. Arterial smooth muscle cell voltage-dependent calcium (CaV1.2) channels are key regulators of vascular contractility. Vascular CaV1.2 channels are activated by membrane depolarization and vasoconstrictor agonists, leading to an increase in intracellular calcium ([Ca2+]i) concentration and vasoconstriction. CaV1.2 channels can undergo enzymatic cleavage, yielding truncated, short-form CaV1.2 channels and a C-terminal protein fragment (CCT). Whether CCT exists in arterial smooth muscle cells and regulates vascular contractility is unclear. This application stems from novel preliminary data indicating that CCT exhibits nuclear localization and attenuates functional CaV1.2 expression in cerebral artery smooth muscle cells. Preliminary data also indicate that vasoconstrictors reduce CCT protein to elevate CaV1.2 channel expression and induce vasoconstriction. The central hypothesis of this proposal is that the CCT controls functional CaV1.2 channel expression and plasma membrane currents in cerebral artery smooth muscle cells. Aim 1 will investigate the hypothesis that the truncated CaV1.2 channel C-terminus inhibits CaV1.2transcription, surface CaV1.2 channel expression, and CaV1.2currents in arterial smooth muscle cells. Aim 2 will examine the hypothesis that vasoconstrictors control CaV1.2 channel expression and activity by modulating the total amount and nuclear localization of CCT in arterial smooth muscle cells. Aim 3 will test the hypothesis that the CCT regulates arterial smooth muscle cell [Ca2+]i, thereby modulating contractility. Techniques to be used include real-time PCR, Western blotting, expression of recombinant CCT, RNA interference, immunofluorescence and immunofluorescence resonance energy transfer (immunoFRET), patch-clamp electrophysiology, calcium imaging, and pressurized artery myography. This research will reveal novel mechanisms of vascular contractility regulation by the CaV1.2 channel C-terminus.